Mitogenic activity of cell wall components from smooth and rough strains of Brucella abortus

Brucella melitensis Wzm/Wzt System: Changes in the Bacterial Envelope Lead to Improved Rev1Δwzm Vaccine Properties

The lipopolysaccharide (LPS) O-polysaccharide (O-PS) is the main virulence factor in Brucella. After synthesis in the cytoplasmic membrane, O-PS is exported to the periplasm by the Wzm/Wzt system, where it is assembled into a LPS. This translocation also engages a bactoprenol carrier required for further biosynthesis pathways, such as cell wall biogenesis. Targeting O-PS export by blockage holds great potential for vaccine development, but little is known about the biological implications of each Wzm/Wzt moiety. To improve this knowledge and to elucidate its potential application as a vaccine, we constructed and studied wzm/wzt single- and double-deletion mutants, using the attenuated strain Brucella melitensis Rev1 as the parental strain. This allowed us to describe the composition of Brucella peptidoglycan for the first time. We observed that these mutants lack external O-PS yet trigger changes in genetic transcription and in phenotypic properties associated with the outer membrane and cell wall. The three mutants are highly attenuated; unexpectedly, Rev1Δwzm also excels as an immunogenic and effective vaccine against B. melitensis and Brucella ovis in mice, revealing that low persistence is not at odds with efficacy. Rev1Δwzm is attenuated in BeWo trophoblasts, does not infect mouse placentas, and is safe in pregnant ewes. Overall, these attributes and the minimal serological interference induced in sheep make Rev1Δwzm a highly promising vaccine candidate.

Peripheral lymphocyte function in dogs with Brucella canis infection

Peripheral lymphocyte function in dogs with Brucella canis infection was evaluated using in vitro lymphocyte stimulation with the mitogens PHA, Con A and PWM, and killed Brucella canis organisms. Bitches with naturally occurring Brucella canis infection were compared to negative controls. There was no difference in the response to Con A and PWM between these two groups. Lymphocytes from infected dogs were less responsive (p less than .05) to PHA than were lymphocytes from controls. There was a significant (p less than .005) difference in response to Brucella canis antigen between the two groups. Lymphocytes from infected dogs were stimulated by Brucella canis antigen, whereas those from controls did not respond.

Immune and mitogenic responses by BALB/c, C3H/HeJ, and nude mice to Brucella abortus bacterin and lipopolysaccharide

The immunogenic and mitogenic properties of Brucella abortus 1119-3 bacterin (BA) and biologically active B. abortus lipopolysaccharide (BA-LPS) were studied using normal and athymic (nude) BALB/c and C3H/HeJ mice. Although BA stimulated 2-mercaptoethanol-sensitive (2-ME-S) primary and secondary antibody responses in all mice, nude mice, in contrast to normal BALB/c and C3H/HeJ mice, did not make substantial 2-mercaptoethanol-resistant (2-ME-R) antibody responses. Similarly, all mice injected with BA-LPS made 2-ME-S primary responses, and the secondary response of thymus-bearing mice contained a substantial 2-ME-R component. Collectively, these observations suggest that although both BA and BA-LPS can stimulate thymus-independent 2-ME-S antibody synthesis, thymus-derived cells are required for optimal immune responses containing a 2-ME-R component. The antibody responses of normal BALB/c and C3H/HeJ mice to BA and BA-LPS were qualitatively and quantitatively similar. Both BA and BA-LPS were mitogenic for spleen cells from normal and nude BALB/c and C3H/HeJ mice but not for thymus cells from normal BALB/c or C3H/HeJ mice, suggesting that both preparations are B-cell mitogens.

Surface macromolecules and virulence in intracellular parasitism: comparison of cell envelope components of smooth and rough strains of Brucella abortus

The surface topography of whole cells and the chemical composition of cell envelopes of a smooth-intermediate strain (45/0) and a rough strain (45/20) of Brucella abortus was examined. Electron microscopy of whole cells and thin sections did not reveal any gross surface difference(s). Only minor quantitative differences were observed in total lipids, proteins, and the murein layer. However, the lipopolysaccharide composition of the two strains was quite different. Both phenol- and water-soluble lipopolysaccharide fractions were obtained from the strain of higher virulence (45/0), whereas only aqueous lipopolysaccharide could be isolated from the rough strain. In addition to being toxic, the phenol-soluble lipopolysaccharide may be a key virulence factor in intracellular survival of B. obortus within phagocytic cells.

Chemical characterization and biological properties of lipopolysaccharides isolated from smooth and rough strains of Brucella abortus

The chemical composition and some of the biological activities of lipopolysaccharides (LPS) extracted from a smooth-intermediate strain (45/0) and a rough strain (45/20) of Brucella abortus have been examined. LPS were found in both the phenolic and aqueous extraction phases of strain 45/0, but only in the aqueous phase of 45/20. The phenolic LPS contained 9- to 16-fold-lower levels of heptose and reduced amounts of dideoxyaldoses compared with aqueous fractions. The major neutral sugars were glucose, galactose, and mannose. beta-Hydroxymyristic-acid, a common marker of enteric LPS, was not detected. Fatty acids present in highest amounts were hydroxylated and nonhydroxylated species with chain lengths of 16, 18, and 20 carbons. Only the phenolic LPS of strain 45/0 exhibited mouse lethality and a curable wasting disease; however, both phenolic and aqueous fractions caused carbohydrate depletion in mice. The toxicity of aqueous LPS could not be potentiated with Pb(OAc)4. These data, coupled with the lack of mitogenic activity for B-lymphocytes, are indicative of the unique structure-function relationships of Brucella LPS.

Influence of the antigenicity of Brucella preparations on modulation of the immune response to sheep erythrocytes

The relationship between the expression of surface antigenicity of inactivated Brucella and the immunostimulant properties on the sheep erythrocyte response was studied in mice. The agglutinogenic Brucella abortus B19S preparation was compared to two non-agglutinogenic preparations (B19R and PB), using the plaque-forming and rosette-forming cell tests. When Brucella and antigen were injected together, only non-agglutinogenic preparations, even used at low doses, were able to increase the plaque-forming and rosette-forming cell responses measured 4 days after immunization. When the interval between the previous injection of non-agglutinogenic preparations and that of the antigen increased or when they were injected 24 h after the antigen, the modification of those two responses was no longer observed. After day 4, for the simultaneous injection of Brucella and antigen, B19S and PB preparations induced the best responses; this effect was dose dependent. Thus, in the present experimental situation, the modification of the day 4 response appeared independent of those of the ensuing days.

Responsiveness of rabbit spleen and appendix cells to bacterial mitogens

Rabbit spleen and appendix cells were used to test the mitogenic activity of a commercial lipopolysaccharide (LPS) preparation from Salmonella typhimurium (Difco), a preparation extracted from it, and cell wall preparations from smooth (45/0) and rough (45/20) strains of Brucella abortus. On the basis of [3H]thymidine incorporation ratios (E/C), that is, the incorporation rate among cells treated with the mitogen relative to that of untreated cells, the extracted LPS and both Brucella cell wall preparations, but not the commercial LPS were potent mitogens for rabbit spleen cells. By the same criterion, only the Brucella cell wall preparation produced a significant, but minimally so, response among appendix cells. The weak responsiveness of appendix cells may be more apparent than real, however, and may not imply a difference in intrinsic susceptibility to mitogens by these two populations, because unstimulated appendix cells incorporated thymidine at 10 times the rate of unstimulated spleen cells. Appendix cells, then, may not be susceptible to further stimulation, even by active mitogens. Therefore, the significance of E/C ratios may be equivocal when materials are assayed for mitogenic activity on lymphoid populations whose basal activity is relatively high.